Global Positioning System Reference
In-Depth Information
The previous examples are still isolated solutions in terms of using only
WSDL-based or WPS-based services. To address the lack of interoperability
between these types of services, the OGC WPS specifi cation encourages
the use of application profi les and supports pointing to associated WSDL
descriptions. In particular, explicit support for WSDL descriptions is a way
to make OGC-based services in the closed geospatial domain available to
mainstream, mass-market web services (mainly based on WSDL), so that
hybrid solutions might be suitable. In this context, a WSDL document can
describe both an entire WPS service and each single contained process.
In the fi rst case, the capabilities document can include a
WSDL
element
pointing to the corresponding WSDL description fi le (URI). The WSDL
document describes the interface of the entire WPS service instance. In the
second case, each contained process description can have its own WSDL
element that points to a specifi c WSDL description fi le, which provides the
functional signature of the WPS process. Schade et al. (2012) discussed on
these WSDL-WPS integration cases.
In March 2011, Lopez-Pellicer et al. (2012) checked the availability
of WPS-based services deployed on the Web. The results however were
disappointing and showed scarce support for WSDL, which seriously
limits interoperability with mass-market WSDL-based web services and
also with BWL and scientifi c workfl ow systems that explicitly support
WSDL-based services.
Some incipient projects are changing this trend though. Yu et al. (2012)
provide WSDL-based descriptions for various kinds of OGC services,
including WPS. These OGC services were orchestrated and executed using
a BPEL-compliant engine, called BPELPower, for a variety of environmental
modeling use cases. This represents a step further, since OGC services are
being orchestrated through WS-BPEL process descriptions. The authors,
however, introduced some enhancements into the BPELPower engine to be
able to interpret the singularities of geospatial-enabled workfl ows.
Indeed, there have been identifi ed in the literature some restrictions
that make geoprocessing services hard to integrate with existing business
process languages (e.g., WS-BPEL) and mass-market web services (e.g.,
WSDL-based services). First, current workfl ow engines provide limited
support for geospatial schemas and sometimes even the parsing and use of
geography markup language (GML)
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may not be always possible. Because
of the inherent complexity of many OGC schemas in terms of complicated
relationships and recursive type defi nitions (Tamayo et al. 2012), business
workfl ow engines are not designed for managing such complexity. Business
workfl ows usually handle simple data items (orders, client records, etc.)
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http://www.opengeospatial.org/standards/gml
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